Factors affecting an ecosystem’s biomass, by Alan and Jack

  

On a hot day about a month ago, my class and I went to a City of Calgary park called Nose Hill Park.   The purpose of going to one of the largest municipal parks in North America was to attain data on the park and its grassland, forest or pond. We were enlightened by the research we did on the grassland, and now we will share that knowledge we gained with you about energy within ecology.  Since energy is such an enormous topic in ecology, only the effect of energy on biomass will be discussed.  

Shown in Figure 1 is a theoretical biomass pyramid.  The rectangles are arranged in an orderly fashion, the rectangle above is smaller than the rectangle below, etc.  However, this is not a true biomass pyramid in nature.  In natural ecosystems, this kind of uniformity just does not occur.  The reason behind the irregularity of biomass pyramids is because of energy.  But, before we get into all of the jargon that can be said, some definitions must first be explained.

Producers: organisms that produce its own food.
            Primary consumers: organisms that consume plants.
            Secondary consumers: organisms that consume primary consumers.
            Tertiary consumers: organisms that consume secondary consumers.
            These different consumers are all on different trophic levels.  Organisms that obtain their energy from the same type of source are on the same trophic level.  For example, producers obtain energy from the sun, while the primary consumers obtain energy from plants.
            I am sure you get the idea.  A much more important definition would be biomass.  Biomass is the weight of organisms after they are dead and dry, within a certain area.  So a biomass pyramid - as seen in Figure 2 - would be a visual representation of the different trophic levels.

These different consumers are all on different trophic levels.  Organisms that obtain their
energy from the same type of source are on the same trophic level.  For example, producers
obtain energy from the sun, while the primary consumers obtain energy from plants.  A much more important definition would be biomass.  Biomass is the weight of organisms after they are dead and dry, within a certain area.  So a biomass pyramid - as seen in Figure 1 - would be a visual representation of the different trophic levels. 

Figure 3.  Our transect.

At Nose Hill Park, we randomly set up a transect of 10 meter by 1 meter within an area that our teacher, Dr. Pike, specified.  Within the transect we found some plants and insects.  We also cut down a sample of 25cm by 25cm of producers, this was used to calculate biomass.  In our biomass pyramid there is an obvious increase in the mass of producers, compared to figure 1.   As well, if looked at closely, the secondary consumer is larger than the primary consumer.  This will be explained below.

Why does biomass have to be a pyramid?  The answer is simple, energy.  When any organisms consume food and obtain nutrition, most of the energy is used to maintain cells.  The cells need to break down the glucose, in foods we eat, in order to make ATP for itself and function normally.  In plants about half of the energy is used to maintain the cell, while only about 11% of energy received from the sun actually joins the food web.  In animals, however, about 80% of energy received from the producers is used in maintenance.  Only 1.6% is used for growth (increasing biomass).  The energy from producers, only 1.6% is used to increase biomass of primary consumers.  So the biomass pyramid of grasslands in Nose Hill Park Figure 2 is scaled correctly.  The producers should have a much more biomass than primary consumers. 

One thing that might have been observed is that secondary consumers have a higher mass than the primary consumers, in Figure 2.  There are two possible explanations for this phenomenon.  The most possible reason is that not enough data was collected.  If a bigger area was used to find insects, the data would have been much more reliable.  The first possibility is much more likely because inverted pyramids usually occur in aquatic environments.  The second possibility, as to why inverted biomass pyramids occur, is that the primary consumers at Nose Hill Park grow, reproduce, and are consumed at a very rapid rate.  The primary consumers are described to have a short turnover time.  The secondary consumers consume the primary consumers very quickly, thus the population of primary consumers never grows.

Here are some photos of the vegetation seen in our transect.

Figure 4. Some plants in our transect.

Figure 5.  Another plant in our transect.

Figure 6. A third plant in our transect.

Figure 7.  The view from our grassland transect.

            We hope that you enjoyed this blog post by Alan and I.  Please also take the time to enjoy some of the other blogs that our fellow classmates thought up.